Carotid body tumours (CBTs) are the most common paragangliomas of the head and neck region. We report an interesting case of CBT which extended in an unusual anatomical fashion presenting as a lump posterior and superficial to sternocleidomastoid muscle thus emphasizing the fact that this diagnosis needs to be considered even with a mass presenting in the posterior triangle of the neck.

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Figure 1. Axial computed tomography of the neck. The image shows the carotid body tumour (labeled red) appearing as an enhancing mass posterior to the sternocleidomastoid muscle with its superficial component overlying the muscle. Normal structures labeled with blue.

A 68-year-old female noticed a 2.5 x 1.5 cm neck lump superficial to the left sternocleidomastoid (SCM) muscle. Relevant past medical history included a lumpectomy for malignant breast neoplasm in 2003. Ultrasound confirmed a solid lesion superficial to the left SCM. CT showed an enhancing lobulated mass lesion splaying the left internal and external carotid artery and compressing the left internal jugular vein, it extended posteriorly curling behind the SCM muscle and terminated in a superficial component overlying the muscle (Figure 1 and 2). In view of her previous history of breast carcinoma core biopsy was performed with histology suggestive of metastatic carcinoma possibly a neuroendocrine tumour. Immunohistochemistry confirmed neuroendocrine differentiation typical for paraganglioma. Twenty four hour urinary catecholamine studies were normal.

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Figure 2. Sagittal computed tomography of the neck demonstrating the carotid body tumour (labeled with red) enveloping the internal jugular vein and curling around the sternocleidomastoid muscle (labeled with blue).

An exploration of her neck was performed with resection of an unusual and very extensive left carotid body tumour measuring 87 x 48 x 17mm and weighing 23grams. The tumour was attached in its usual manner to the carotid bifurcation and the adjacent internal and external carotid vessels. It extended to envelop the internal jugular vein, then curled posterior to the SCM and hooked back over superficial to the muscle. An extensive lymph node dissection was performed because of the possibility of a malignant variant. Cranial nerves X, XI and XII were identified and preserved. Histology confirmed features of a paraganglioma with no evidence of metastatic disease in the lymph nodes. The patient was noted to be hypertensive on follow up visits though repeat catecholamine assays were normal.

The carotid body is a cluster of chemoreceptor cells located at the carotid bifurcation. Paragangliomas are tumours of neural crest origin and carotid body tumours (CBTs) are the commonest cervical paragangliomas accounting for greater than 50 percent of cases [1]. They are histologically similar to pheochromocytomas; most are sporadic but around 10 to 50 percent of cases are a component of inherited paraganglioma syndromes [1] [2]. Most CBTs are benign with around 10% showing malignant potential [2]. They usually present as asymptomatic neck masses anterior to the SCM at the level of the hyoid bone corresponding to the carotid bifurcation. They may or may not be associated with pain with large tumours producing local compressive symptoms. Rarely paragangliomas of the head and neck may function similar to a pheochromocytoma causing symptoms such as headache, palpitations, diarrhoea, flushing and hypertension. Benign or malignant potential is based on clinical behaviour; histomorphologic features alone may not clearly differentiate benign from malignant tumours [3]. Clear evidence of malignant potential is based on invasion of adjacent structures, presence of metastatic disease or tumour recurrence [2] [3].

Imaging modalities include colour duplex ultrasonography (CDUS), CT angiography and MR imaging. Typically, they cause splaying of the carotid bifurcation with a confused pattern of tumour vascularisation on duplex scanning and enhancement on CT and MR imaging. Parangangliomas have a high density of somatostatin type two receptors; therefore, octreotide scintigraphy may be used to confirm somatostatin receptor activity thus determining the nature, localization and malignant potential of the tumour [4]. Incisional biopsy is contra-indicated because their rich vascular supply increases risk of haemorrhage and fibrosis at the operative site rendering resection difficult [5].

Treatment is early surgical intervention with complete resection of the tumour and adequate regional lymph node sampling. This prevents further growth and involvement of adjacent neurovascular structures. The role of pre-operative embolization, chemotherapy and radiotherapy is controversial. Long term follow up is necessary as metastasis may develop years post treatment.

This case was unusual in its direction of progression and its presentation as a neck swelling in the posterior triangle of the neck, it tracked behind SCM with its tail sitting superficial to the muscle and despite this feature no evidence of malignancy was found on complete resection of the tumour and adjacent lymph nodes. This enables us to familiarize ourselves with different presentation, surgical findings and anatomical variants of CBTs.

All authors have seen and approved the manuscript and contributed significantly to the work. The manuscript has not been previously published nor is being considered for publication elsewhere.